JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track July 30, 2012
Expires: January 31, 2013
JSON Web Key (JWK)draft-ietf-jose-json-web-key-05
Abstract
A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data
structure that represents a public key. This specification also
defines a JSON Web Key Set (JWK Set) JSON data structure for
representing a set of JWKs. Cryptographic algorithms and identifiers
for use with this specification are described in the separate JSON
Web Algorithms (JWA) specification.
Status of this Memo
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This Internet-Draft will expire on January 31, 2013.
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Internet-Draft JWK July 20121. Introduction
A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) [RFC4627]
data structure that represents a public key. This specification also
defines a JSON Web Key Set (JWK Set) JSON data structure for
representing a set of JWKs. Cryptographic algorithms and identifiers
for use with this specification are described in the separate JSON
Web Algorithms (JWA) [JWA] specification.
Goals for this specification do not include representing private
keys, representing symmetric keys, representing certificate chains,
representing certified keys, and replacing X.509 certificates.
JWKs and JWK Sets are used in the JSON Web Signature (JWS) [JWS] and
JSON Web Encryption (JWE) [JWE] specifications.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in Key words for use in
RFCs to Indicate Requirement Levels [RFC2119].
2. Terminology
JSON Web Key (JWK) A JSON data structure that represents a public
key.
JSON Web Key Set (JWK Set) A JSON object that contains an array of
JWKs as a member.
Base64url Encoding The URL- and filename-safe Base64 encoding
described in RFC 4648[RFC4648], Section 5, with the (non URL-
safe) '=' padding characters omitted, as permitted by Section 3.2.
(See Appendix C of [JWS] for notes on implementing base64url
encoding without padding.)
Collision Resistant Namespace A namespace that allows names to be
allocated in a manner such that they are highly unlikely to
collide with other names. For instance, collision resistance can
be achieved through administrative delegation of portions of the
namespace or through use of collision-resistant name allocation
functions. Examples of Collision Resistant Namespaces include:
Domain Names, Object Identifiers (OIDs) as defined in the ITU-T
X.660 and X.670 Recommendation series, and Universally Unique
IDentifiers (UUIDs) [RFC4122]. When using an administratively
delegated namespace, the definer of a name needs to take
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reasonable precautions to ensure they are in control of the
portion of the namespace they use to define the name.
3. Example JSON Web Key Set
The following example JWK Set contains two public keys represented as
JWKs: one using an Elliptic Curve algorithm and a second one using an
RSA algorithm. The first specifies that the key is to be used for
encryption. Both provide a Key ID for key matching purposes. In
both cases, integers are represented using the base64url encoding of
their big endian representations. (Long lines are broken are for
display purposes only.)
{"keys":
[
{"alg":"EC",
"crv":"P-256",
"x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
"y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
"use":"enc",
"kid":"1"},
{"alg":"RSA",
"mod": "0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx
4cbbfAAtVT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMs
tn64tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FDW2
QvzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n91CbOpbI
SD08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINHaQ-G_xBniIqb
w0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw",
"exp":"AQAB",
"kid":"2011-04-29"}
]
}
4. JSON Web Key (JWK) Format
A JSON Web Key (JWK) is a JSON object containing specific members, as
specified below. Those members that are common to all key types are
defined below.
In addition to the common parameters, each JWK will have members that
are specific to the key being represented. These members represent
the parameters of the key. Section 5 of the JSON Web Algorithms
(JWA) [JWA] specification defines multiple kinds of public keys and
their associated members.
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The member names within a JWK MUST be unique; objects with duplicate
member names MUST be rejected.
Additional members MAY be present in the JWK. If present, they MUST
be understood by implementations using them. Member names used for
representing key parameters for different kinds of keys need not be
distinct. Member names SHOULD either be registered in the IANA JSON
Web Key Parameters registry Section 6.1 or be URIs that contain a
Collision Resistant Namespace.
4.1. "alg" (Algorithm Family) Parameter
The "alg" (algorithm family) member identifies the cryptographic
algorithm family used with the key. "alg" values SHOULD either be
registered in the IANA JSON Web Key Algorithm Families registry [JWA]
or be a URI that contains a Collision Resistant Namespace. The "alg"
value is a case sensitive string.
A list of defined "alg" values can be found in the IANA JSON Web Key
Algorithm Families registry [JWA]; the initial contents of this
registry is the values defined in Section 5.1 of the JSON Web
Algorithms (JWA) [JWA] specification.
Additional members used with these "alg" values can be found in the
IANA JSON Web Key Parameters registry Section 6.1; the initial
contents of this registry is the values defined in Sections 5.2 and
5.3 of the JSON Web Algorithms (JWA) [JWA] specification.
4.2. "use" (Key Use) Parameter
The "use" (key use) member identifies the intended use of the key.
Values defined by this specification are:
o "sig" (signature)
o "enc" (encryption)
Other values MAY be used. The "use" value is a case sensitive
string. This member is OPTIONAL.
4.3. "kid" (Key ID) Parameter
The "kid" (key ID) member can be used to match a specific key. This
can be used, for instance, to choose among a set of keys within the
JWK during key rollover. The interpretation of the "kid" value is
unspecified. Key ID values within a JWK Set need not be unique. The
"kid" value is a case sensitive string. This member is OPTIONAL.
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When used with JWS or JWE, the "kid" value MAY be used to match a JWS
or JWE "kid" header parameter value.
In some contexts, different keys using the same Key ID value might be
present, with the keys being disambiguated using other information,
such as the "alg" or "use" values. For example, imagine "kid" values
like "Current", "Upcoming", and "Deprecated", used for key rollover
guidance. One could apply a label to all keys where the
classification fits. If there are multiple "Current" keys, then in
this example, they might be differentiated either by having different
"alg" or "use" values, or some combination of both. As one example,
there might only be one current RSA signing key and one current
Elliptic Curve signing key, but both would be "Current".
5. JSON Web Key Set (JWK Set) Format
A JSON Web Key Set (JWK Set) is a JSON object that contains an array
of JSON Web Key values as the value of its "keys" member.
The member names within a JWK Set MUST be unique; objects with
duplicate member names MUST be rejected.
Additional members MAY be present in the JWK Set. If present, they
MUST be understood by implementations using them. Parameters for
representing additional properties of JWK Sets SHOULD either be
registered in the IANA JSON Web Key Set Parameters registry
Section 6.2 or be a URI that contains a Collision Resistant
Namespace.
5.1. "keys" (JSON Web Key Set) Parameter
The value of the "keys" (JSON Web Key Set) member is an array of JSON
Web Key (JWK) values. This member is REQUIRED.
6. IANA Considerations
The following registration procedure is used for all the registries
established by this specification.
Values are registered with a Specification Required [RFC5226] after a
two week review period on the [TBD]@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Expert(s)
may approve registration once they are satisfied that such a
specification will be published.
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Registration requests must be sent to the [TBD]@ietf.org mailing list
for review and comment, with an appropriate subject (e.g., "Request
for access token type: example"). [[ Note to RFC-EDITOR: The name of
the mailing list should be determined in consultation with the IESG
and IANA. Suggested name: jose-reg-review. ]]
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s),
and should direct all requests for registration to the review mailing
list.
6.1. JSON Web Key Parameters Registry
This specification establishes the IANA JSON Web Key Parameters
registry for reserved JWK parameter names. The registry records the
reserved parameter name and a reference to the specification that
defines it. This specification registers the parameter names defined
in Section 4.
6.1.1. Registration Template
Parameter Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted.
Change Controller:
For standards-track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
e-mail address, home page URI) may also be included.
Specification Document(s):
Reference to the document that specifies the parameter, preferably
including a URI that can be used to retrieve a copy of the
document. An indication of the relevant sections may also be
included, but is not required.
6.1.2. Initial Registry Contents
o Parameter Name: "alg"
o Change Controller: IETF
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o Specification Document(s): Section 4.1 of [[ this document ]]
o Parameter Name: "use"
o Change Controller: IETF
o Specification Document(s): Section 4.2 of [[ this document ]]
o Parameter Name: "kid"
o Change Controller: IETF
o Specification Document(s): Section 4.3 of [[ this document ]]
6.2. JSON Web Key Set Parameters Registry
This specification establishes the IANA JSON Web Key Set Parameters
registry for reserved JWK Set parameter names. The registry records
the reserved parameter name and a reference to the specification that
defines it. This specification registers the parameter names defined
in Section 5.
6.2.1. Registration Template
Parameter Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted.
Change Controller:
For standards-track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
e-mail address, home page URI) may also be included.
Specification Document(s):
Reference to the document that specifies the parameter, preferably
including a URI that can be used to retrieve a copy of the
document. An indication of the relevant sections may also be
included, but is not required.
6.2.2. Initial Registry Contents
o Parameter Name: "keys"
o Change Controller: IETF
o Specification Document(s): Section 5.1 of [[ this document ]]
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Internet-Draft JWK July 20127. Security Considerations
All of the security issues faced by any cryptographic application
must be faced by a JWS/JWE/JWK agent. Among these issues are
protecting the user's private key, preventing various attacks, and
helping the user avoid mistakes such as inadvertently encrypting a
message for the wrong recipient. The entire list of security
considerations is beyond the scope of this document, but some
significant concerns are listed here.
A key is no more trustworthy than the method by which it was
received.
Per Section 4.3, applications should not assume that "kid" values are
unique within a JWK Set.
The security considerations in XML DSIG 2.0
[W3C.CR-xmldsig-core2-20120124], about public key representations
also apply to this specification, other than those that are XML
specific.
8. Open Issues
[[ to be removed by the RFC editor before publication as an RFC ]]
The following items remain to be considered or done in this draft:
o There was a request to define the key use value "both". This
would seem to be semantically redundant, since omitting a key use
value effectively allows unconstrained use of the key. For what
it's worth, omitting the use parameter is how XMLDSIG expresses
the same thing, so we're currently parallel to XMLDSIG.
Furthermore, legitimizing the use of a single key for both signing
and encryption seems like it may be a bad idea, since there's a
potential vulnerability with using the same key for both signing
and encryption.
9. References9.1. Normative References
[JWA] Jones, M., "JSON Web Algorithms (JWA)", July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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o Indented artwork elements to better distinguish them from the body
text.
-04
o Refer to the registries as the primary sources of defined values
and then secondarily reference the sections defining the initial
contents of the registries.
o Normatively reference XML DSIG 2.0 [W3C.CR-xmldsig-core2-20120124]
for its security considerations.
o Added this language to Registration Templates: "This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted."
o Described additional open issues.
o Applied editorial suggestions.
-03
o Clarified that "kid" values need not be unique within a JWK Set.
o Moved JSON Web Key Parameters registry to the JWK specification.
o Added "Collision Resistant Namespace" to the terminology section.
o Changed registration requirements from RFC Required to
Specification Required with Expert Review.
o Added Registration Template sections for defined registries.
o Added Registry Contents sections to populate registry values.
o Numerous editorial improvements.
-02
o Simplified JWK terminology to get replace the "JWK Key Object" and
"JWK Container Object" terms with simply "JSON Web Key (JWK)" and
"JSON Web Key Set (JWK Set)" and to eliminate potential confusion
between single keys and sets of keys. As part of this change, the
top-level member name for a set of keys was changed from "jwk" to
"keys".
o Clarified that values with duplicate member names MUST be
rejected.
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